Interesting. I was under the impression that ground detection has been _required_ for all ungrounded power systems for a very long time...but I just took a look at my copy of the 2002 code, and the sentence that Don mentions is not there. Ungrounded systems are permitted in several instances in 250.21, but only 250.21(3) requires ground detectors. The general permission to have ungrounded systems (250.21(5) which says 'other systems not required to be grounded by 250.20(B)') appears to have been added in the 2002 code.
In the 2005 version of the code there is an explicit requirement for ground detectors for every ungrounded system mentioned in 250.21.
Does anyone know the history of this? Were ground detectors really not required for most ungrounded systems prior to 2005, or did the requirement get accidentally lost in the 2002 code, and returned in the 2005 code, or is it someplace else.
-Jon
